The planner simplifies boolean comparisons such as "x = true" and
"x = false" down to "x" and "NOT x" respectively, to have a canonical
form to ease comparisons. However, if we want to use an index on x,
the index AM APIs require us to reconstitute the comparison-operator
form of the indexqual. While that works, in bitmap indexscans the
canonical form of the qual was emitted as a "filter" condition
although it really only needs to be a "recheck" condition, because
create_bitmap_scan_plan didn't recognize the equivalence of that
form with the generated indexqual. booleq() is pretty cheap so that
likely doesn't make very much difference, but it's unsightly so
let's clean it up.
To fix, add a case to predicate_implied_by() to recognize the
equivalence of such clauses. This is a relatively low-cost place to
add a check, and perhaps it will have additional use cases in future.
Richard Guo and Tom Lane, per discussion of bug #17618 from Sindy
Senorita.
Discussion: https://postgr.es/m/17618-7a2240bfaa7e84ae@postgresql.org
The planner has to special-case indexes on boolean columns, because
what we need for an indexscan on such a column is a qual of the shape
of "boolvar = pseudoconstant". For plain bool constants, previous
simplification will have reduced this to "boolvar" or "NOT boolvar",
and we have to reverse that if we want to make an indexqual. There is
existing code to do so, but it only fires when the index's opfamily
is BOOL_BTREE_FAM_OID or BOOL_HASH_FAM_OID. Thus extension AMs, or
extension opclasses such as contrib/btree_gin, are out in the cold.
The reason for hard-wiring the set of relevant opfamilies was mostly
to avoid a catalog lookup in a hot code path. We can improve matters
while not taking much of a performance hit by relying on the
hard-wired set when the opfamily OID is visibly built-in, and only
checking the catalogs when dealing with an extension opfamily.
While here, rename IsBooleanOpfamily to IsBuiltinBooleanOpfamily
to remind future users of that macro of its limitations. At some
point we might want to make indxpath.c's improved version of the
test globally accessible, but it's not presently needed elsewhere.
Zongliang Quan and Tom Lane
Discussion: https://postgr.es/m/f293b91d-1d46-d386-b6bb-4b06ff5c667b@yeah.net
Tom Lane
Teodor Sigaev